Changes in planet orbits as a star (eg. the Sun) decreases is mass.

In summary, the conversation revolves around the understanding of how the mass of the sun affects the orbit of planets and the Earth. It is explained that according to Newtonian mechanics, the same result can be arrived at without the use of relativity. However, it is also mentioned that the small decrease in the sun's mass over time can lead to a slight increase in the Earth's orbit. The conversation then delves into the concept of gravitational waves and how they can cause a decrease in the orbit radius, leading to a debate on whether the orbit radius increases or decreases under GR. The conversation ends with one participant expressing surprise at the difference in outcomes between Newtonian and GR in regards to the orbit radius.
  • #1
Jus
17
0
Hi,

I'm actually a Design Engineer but I find the topic of Relativity extremely interesting and I was wondering if somebody could give me some guidance on this.

If Planets and Stars (due to their mass) 'warp' Space-Time then this means that our Sun distorts the fabric of space just like a heavy ball on a trampoline... Have I understood that right?

Ok, presuming that the above is correct, the orbits of the planets around the sun follow this distortion just like a ball rolling around a sink bowl... Does that sound right?

Again assuming I've understood the above points correctly, if the Sun is decreasing in mass all of the time then clearly the amount of distortion caused by the mass of the Sun on the fabric of space is decreasing... Does that sound right?

If all of the above is true, then wouldn't this mean that the planets following the path of the distortion (the balls rolling around the sink) would actually be moving away from the Sun as the 'sink' is effectively becoming slightly flatter due to the reduction in mass of the Sun?

Sorry if this sounds like a stupid question but it's been bothering me for the last few days!

Thanks in advance.

Jus
 
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  • #2
Yes, but you don't need relativity to arrive at this result. Newtonian mechanics says the same thing will happen.
 
  • #3
Yes planets are moving their orbits as sun losses mass. But numbers are almost insignificant. When you add both solar winds and mass-energy conversion of sun, I think that you get about one Earth's own radius increase in Earth's orbit over entire life of sun so far.
 
  • #4
S.Vasojevic said:
Yes planets are moving their orbits as sun losses mass. But numbers are almost insignificant. When you add both solar winds and mass-energy conversion of sun, I think that you get about one Earth's own radius increase in Earth's orbit over entire life of sun so far.


Thanks for the answer. Sorry if it sounded like a stupid question, I didn't realize that the change in Orbit would be so insignificant.
 
  • #6
The sun losses about 10^-13 of it's mass/year
This increases the Earth-Sun distance at the same rate.
But since the Earth-Sun distance is 150million km this is only about 1cm/year
 
  • #7
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  • #8
heldervelez said:
On the contrary !
Everyone believes that the orbit radius must increase (even I do !)
How to explain the http://en.wikipedia.org/wiki/Gravitational_wave#Orbital_decay_from_gravitational_radiation"?
The orbit must vary in the same way as the conditions are similar (loss of mass/energy and non relativistic velocities).

We say: radius increase.
Other say: radius decrease.

Why ?

Consider the Earth orbiting the Sun. What would happen to the distance between the Earth and the Sun if the Earth's kinetic energy were gradually siphoned off?
 
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  • #9
George Jones said:
Consider the Earth orbiting the Sun. What would happen to the distance between the Earth and the Sun if the Earth's kinetic energy were gradually siphoned off?

I say : radius increase (and We say as seen above).

How should I understand the 'assumed' orbit decay due to radiation of gravitacional waves (masss loss) ?
 
  • #10
heldervelez said:
I say : radius increase (and We say as seen above).

No Newtonian gravity, or, equivalently, Kepler's third law, can be used to show that the distance decreases. I would do this, but, right now, my three-year-old is demanding that I read to her.
 
  • #11
I agree with you George Jones and I have no need to see a 'proof'.
My surprise is that under GR we can not have such a different result.
Newtonian is an approximation of GR then I am prepared to sentences like this:
the rate of increase of radius on GR is more (or less, not important to the discusssion) than under Newtonian gravitation.
but never like this:
under Newtonian: increase of radius ; under GR decrease of radius.

I can not understand such a different outcome.
 

1. How does a decrease in a star's mass affect the orbit of planets?

The decrease in a star's mass can significantly affect the orbits of planets. As the star's mass decreases, the gravitational force it exerts on the planets decreases as well. This can cause the planets to move further away from the star or even escape its gravitational pull entirely, resulting in changes in their orbits.

2. Will the decrease in a star's mass cause planets to collide with each other?

No, the decrease in a star's mass will not cause planets to collide with each other. This is because the gravitational force between the planets themselves is much weaker than the force exerted by the star. Therefore, any changes in the orbits of planets due to a decrease in the star's mass will not cause them to collide.

3. How will the decrease in a star's mass impact the habitability of planets?

The decrease in a star's mass can affect the habitability of planets in multiple ways. If the decrease is significant enough to cause a planet to move out of the star's habitable zone, it could potentially make the planet too cold or too hot for life to exist. Additionally, changes in the planet's orbit could also affect its climate and atmospheric conditions, further impacting its habitability.

4. Can a decrease in a star's mass result in changes in the length of a planet's year?

Yes, a decrease in a star's mass can result in changes in the length of a planet's year. This is because the time it takes for a planet to complete one orbit around the star is directly proportional to the mass of the star. Therefore, as the star's mass decreases, the length of a planet's year will also decrease.

5. Will the decrease in a star's mass have any effect on the shape of a planet's orbit?

Yes, a decrease in a star's mass can impact the shape of a planet's orbit. This is because the force of gravity from the star affects the shape of the orbit. As the star's mass decreases, the shape of the orbit may become more elliptical or even change to a more circular shape depending on the specific conditions and interactions with other planets in the system.

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